[27] THE OSTEOLOGY OP AMIA CALVA. 773 



investigations of the topographical relations of the labyrinth region in 

 the skulls of fishes, and the determination of the sound-conducting 

 channels according to purely physical principles. The prevailing idea 

 at present is that, in fishes generally, no special channels for the con- 

 duction of sounds have been differentiated ; that, on the contrary, an 

 entirely evenly-proportioned conduction takes place through the bones 

 of the skull, and above all through its cover-bones. Specialized auxil- 

 iary apparatus of the ear, intended for the conduction of the sound- 

 waves to the labyrinth, with the least possible loss, are said to appear 

 first in the class Amphibia j this is positively erroneous. A superficial 

 review of the majority of fishes demonstrates the improbability of this 

 assumption. In the vast majority of fishes the bones w the cranium at 

 no place enter into contact with the surrounding medium, but are sepa- 

 rated from it by extraordinarily poor sound-conductors, by a thick 

 swardy skin, and frequently even by powerful layers of muscles, so 

 that the conduction of the sound-waves directly through the bones of 

 the head can be counted on in a comparatively very small number of 

 fishes only, as in those whose heads are covered by naked bone-shields. 

 The possibility that it takes place through a general conduction on the 

 part of the bones must be absolutely set aside for the vast majority of 

 fishes, and we will have to look about us for other channels of conduc- 

 tion. 



Such a channel has been found for us by Hasse^^ in the Olupeidse. He 

 found that that portion of the auditory capsule, which bounds the sac- 

 culus laterally, forms the inner wall of the gill cavity, and so enables 

 the sound-waves to infringe upon the sacculus through this space. These 

 observations are correct, only that Hasse has erred in that he regards 

 the intimate relations of the labyrinth to the gill cavity as confined to 

 the Clupeidae, whereas it occurs in the majority of osseous fishes. In a 

 large number of these latter, representatives of the most widely sepa- 

 rated families, I found almost without exception that the anterior supe- 

 rior apical recess of the gill cavity lies in close juxtaposition with the 

 labyrinth region of the skull, consequently at this point the water pres- 

 ent in the gill cavity is only separated from the thin, lateral osseous or 

 cartilaginous wall of the labyrinth by a thin mucous membrane. In 

 numerous cases, in which the sacculus with its otoliths is fully devel- 

 oped and forms a lateral jutting bulla on the skull, this bulla almost 

 without exception projects into the giU cavity, and in many instances 

 can be felt from the gill cavity by the finger with great ease. Yet I 

 would have it distinctly understood that in most cases it is not the sac- 

 culus alone that has this relation to the gill cavity, but that the utricu- 

 lus also enjoys a similar relation, and so it is not admissible here to 



39 C. Hasse, Anatomische Studien; Suppl. Die vergleichende Morphologie dea hautigen 

 Gehorgange der Wirlelthiere, 1873, page 53. [C. Hasse, Anatomical Studies; Suppl. 

 The comparative morphology of the membranous auditory passage of the vertebrated 

 animals, 1873, page 53.] 



